1. Field of the Invention
The present invention relates to methods and systems for saving energy by reducing the intensity of traffic signal lights at selected times when less intensity is required.
2. Description of the Prior Art
The human eye adjusts its light receiving capabilities as a function of the light received by the eye and the angles in which the light is coming. In effect, during daytime hours, the opening into the eye is smaller and a greater amount of light is necessary in order to achieve the same relative effect. At night, or when there is less light, a comparatively smaller amount of light will have the same subjective effect. This capability of the human eye to open wider in dim light opens the way to save a substantial amount of energy. Among the ways that energy can be saved includes the reduction of the intensity of traffic signal lights during non-daylight hours. The power saving per intersection in major cities will average about 1,000 kilowatt hours per intersection (having a cost of perhaps $90.00) per year. Since there are about 100,000 appropriate intersections in the U.S., the saving would be probably substantially in excess of 100 million kilowattt hours per year.
The control at any one intersection could be by means of a light intensity tester or by timer or by a signal transmitted from a central point.
The prior art includes at least two types of dimmers. A model PC 110 manufactured by 3M Corporation U.S. Pat. No. 3,500,455 is approximately 11/2 inches.times.3/4 inches.times.23/4 inches and is potted with clear epoxy/polyurethane. It has a 110/130 vac 60 Hz 1.5 amp Tungsten rating. It is used to dim one signal manufactured by 3M and contains an electric eye.
The dimmer is a conventional phase shift device where power is reduced to the lamp by delaying the start of conduction on both positive and negative half cycles, depending on ambient light conditions. When it is very dark, the conduction angle is somewhat less than 90 degrees (it may be 30 degrees to 40 degrees). Unfortunately, this system has a bad feature in that it introduces a substantial amount of noise into the system. While a filter network in the module reduces the noise, it is very difficult to filter the 10 amp load allowed for each load switch. This technique is, accordingly, not feasible for an entire intersection.
McMorrow Eng Co has a dimmer built into their load switch model LS-12D. This dimmer feature is activated by connecting pin 4 to logic ground, thereby applying plus 24 VDC to an electomechanical relay. This relay in turn switches a bridge circuit feeding what appears to be a SCR driver/power triac combination. When the relay is energized, the power output to the lamp load is half-wave, (positive half-cycles only). This reduces power consumption approximately 50 percent but introduces a DC component on the power line. This causes substantial problems for the power company if the system is used extensively in an area. The positive half-cycle which is used by MEG during the dimmer mode was probably chosen so that it would enable older model NEMA conflict monitors to detect conflicts, since these old monitors worked only on the positive half-cycle of the power lines.